Abstract American society is experiencing an epidemic of obesity. Because of the key role of the hypothalamus in controlling body weight, the long-term objective of this research has been to examine arcuate nucleus hypothalamic genes involved in energy homeostasis. The proposed studies focus upon the hypothalamic melanocortinergic system which has become a focal point for basic research and drug development. That system contains alpha melanocyte-stimulating hormone (-MSH) and melanocortin receptor (MCR) subtypes MC3R and MC4R. -MSH is a potent satiety-inducing factor that mediates its effects by binding and activating MC3R and MC4R. A continuing analysis of hypothalamic gene expression changes has identified ankyrin repeat and SOCS box containing protein 4 (Asb-4) as a very promising investigative target. Asb-4 is an important intracellular regulatory protein in CNS energy homeostatic circuits that is highly regulated in hypothalamic neurons. The proposed research is contained in four specific aims: 1) To examine alternative melanocortin signaling pathways. We hypothesize that MC3R and MC4R activate mitogen-activated protein kinase signaling pathways in addition to well- recognized cyclic AMP-dependent processes in hypothalamic neurons. 2) To determine the role of melanocortin signaling in regulation of c-Jun NH2-terminal kinase (JNK). We hypothesize that MC3R and MC4R, via Asb-4, regulate arcuate nucleus JNK activity. 3) To elucidate transcriptional regulation of Asb-4. We hypothesize that Asb-4 expression in the hypothalamus is regulated by the melanocortinergic peptide, -MSH. 4) To determine the role Asb-4 in feeding behavior. We hypothesize that ankyrin repeat and SOCS box containing protein 4 is a crucial intracellular protein in hypothalamic neurons. We hypothesize that directed overexpression of Asb-4 in hypothalamic proopiomelanocortin neurons will decrease food intake, increase energy expenditure and confer resistance to high fat diet-induced obesity.